Apparatus for treating metal



June 11, 1946.

R. A. BIERWIRTH ET AL 2,401,899

APPARATUS FOR TREATING METAL Filed April 30', 1942 3nventors Rudolph H. Birwirth & E yril MHaylar CAM (Ittomeg Patented June 11, 1946 UNITED STATES PATENT OFFICE APPARATUS FOR TREATING METAL Rudolph A. Bierwirth, Haddon Heights, and Cyril N. Hoyler, Audubon, N. J., assignors to Radio Corporation of America Application April 30, 1942, Serial No. 441,106

2 Claims. 1

This invention relates to the treatment of metals, and more particularly to an improved apparatus for heating steel or other ferrous metal prior to tempering thereof.

Resilient metals, in strip or sheet form, are used in many applications where advantage is taken of the springiness of the material. One such use, for example, is in certain types of condensers employed in radio apparatus and the like. Heretofore, thin leaves of brass or phosphor bronze have usually been used for the electrodes in such condensers, but sheet steel, if properly hardened and tempered, may be used equally well and, in fact, offers certain advantages over brass and phosphor bronze when considered from the standpoints of long life and efliciency.

To be practical, the material should be hardened and tempered in strip form to such a degree that it may be readily formed and yet have proper springiness so that further heat treatment of the parts is unnecessary. Now, it has been proposed, heretofore, to treat sheet steel in furnaces for this purpose, but this involves, among other disadvantages, those requiring considerable space in which to install suitable furnaces and of being relatively ineflicient.

The primary object of our present invention is to provide an improved apparatus for treating steel which will not be subject to the limitations imposed by and the disadvantages found in conventional furnaces employed for this purpose.

More particularly, it is an object of our present invention to provide an improved apparatus for treating sheet or strip steel or the like to heat it continuously to a uniform temperature suitable for hardening and tempering thereof.

Another object of our present invention is to provide an improved apparatus for rapidly heating ferrous metals, particularly in strip form, to render the same hard prior to tempering it.

Still another object of our present invention is to provide an improved coupling coil for heating the material to be treated with the aid of radio frequency energy.

It is also an object of our present invention to provide an improved apparatus as aforesaid which is characterized by simplicity and which is both economical and hi hly efhcient in use.

When steel or other ferrous material is placed in a rapidly alternating magnetic field, it is heated by hysteresis and eddy current losses.

When the temperature reaches the Curie point, that is, the point at which the permeability becomes unity (about 1300 F. for strip steel having a carbon content of about 0.5 percent), the hysteresis loss becomes zero. Consequently, induction heating above 1300 F. must be accomplished by eddy current losses. If a thin strip of steel is placed in a strong alternating magnetic field and parallel to it, the eddy current losses will be small compared to the hysteresis losses, the latter predominating until the Curie point is reached. when the temperature reaches 1300 F., the Curie point, the hysteresis losses disappear and the temperature will not increase appreciably unless the field is made very strong, If the steel strip is placed in a field normal to its width, the eddy current losses will generally predominate and it will be diificult to obtain uniform heating because of the tendency for the eddy currents to flow near the edges of the strip.

In accordance with our present invention, a strip of steel or other magnetic material is heated with the aid of radio frequency energy by means of a coupling coil designed to heat the strip by predominant hysteresis 1osses to the Curie point of 1300" F. and thereafter to the tempering temperature of about 1500" F. by eddy current losses. The heating or coupling coil consists essentially of a Winding adapted to carry radio frequency current and consisting of one or more turns through which the steel strip to be treated is passed in a direction parallel to the axis of the coil, so that the rapidly alternating magnetic field set up by this coil extends in a direction parallel to the strip and effects heating of the strip to the Curie point by hysteresis losses resulting therefrom, The inductor coupling coil also includes another winding of at least a partial turn arranged to subject the steel strip to a second magnetic field which extends in a direction at right angles to the strip thereby to heat it to the hardening temperature by predominant eddy current losses. In this manner, the strip is quickly and efliciently heated to its hardening temperature, after which it may be quenched and again heated to the tempering temperature.

The novel features that we consider characteristic of our invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description of two embodiments thereof, when read in connection with the accompanying drawing, in which Figure 1 is a top plan view of one form of coupling coil constructed according to our present invention;

Figure 2 is an end elevation thereof;

Figure 3 is a side elevation thereof;

Figure 4 is a top plan view of another form of coupling coil in accordance with our present invention;

Figure is an end elevation of the latter form of our invention; and

Figure 6 is a diagrammatic view of an arrangement for the continuous treatment of strip steel in accordance with our present invention.

Referring more particularly to the drawing, wherein similar reference characters designate corresponding parts throughout, there is shown a strip I of steel or other ferrous or magnetic material in association with an inductor coupling coil 3 adapted to be connected to a suitable source of radio frequency energy, such as a radio frequency oscillation generator (not shown). The coupling coil 3 is preferably made of hollow tubing for the circulation of a cooling fluid therethrough and has a pair of turns 3a which encircle the strip I and a loop or nose 3b extending from one of the end turns of the winding 3a. The loop 317 is arranged substantialy parallel to the axis of the turns 3a as well as the strip I and in close proximity to the turns 3a, the axis of the loop 31) being substantially normal to that of the turns 3a. As can be seen from Figures 1 to 3, the steel strip I passes through the turns 3a which set up a high frequency alternating magnetic field which produces in the strip I hysteresis losses sufficient to heat the strip to the Curie point. The loop 3b is serially connected to the turns 3a and sets up a high frequency alternating magnetic field which xtends in a direction substantially normal to the strip I and to the field set up by the windings 3a,

CROSS REFERtNiJt the field set up by the loop 3b serving to further heat the strip I by eddy current losses to a temperature of about 1500 F. Connection may be made to the radio frequency oscillator by means of a pair of electrodes 5 insulated from each other by a suitable insulating strip 1 and suitably secured to conductive blocks 9 which support the heating coil 3.

It will be apparent that, while two complete turns 3a have been shown as encircling the strip I, this portion of the heating coil may be made of only one or any other suitable number of turns. Similarly, the'loop or nose 3b may be made of one or more complete turns instead of consistin of a partial turn, as shown. The important thing is that the turn or turns 3a set up a field which heats the strip I to the Curie point predominantly by hysteresis losses, whereas the loop 3b is so oriented that it sets up a field which thereafter heats the strip I predominantly by eddy current losses above the Curie point. By adjusting the shape of the loop 317 and its proximity to the strip I, it is possible to attain quite uniform heating. A suitable cooling fiuid, such as water, circulated through the coil 3, prevents it from becoming excessively hot.

In the form of our invention shown in Figs. 4 and 5, the heating coil I3 is made of a strip of sheet material bent to provide a single turn, elongated winding I3a which encircles the strip I. Preferably, although not necessarily, the winding I3a is formed rather fiat or shallow, as shown in Figure 5. The winding I 3a is formed adjacent one of its ends with an opening IS with which communicates a slit II extending from the opposite edge of the coil I3. As radio frequency current flows from one electrode or terminal I9 to the other of the cOil I3 and through the winding I3a, it sets up a high frequency magnetic field parallel to the strip I to heat the strip by hysteresis losses to the Curie point. The current also passes in a path around the opening I5, and this sets up a second high frequency magnetic field which extends in a direction normal to the strip I, thereby heating the strip further by eddy current losses. If desired, the coupling coll I! may also be made of tubing or the like to permit passage of a cooling fluid therethrough.

In Fig. 6, we have shown diagrammatically an arrangement for utilizing any of the forms of heating coils constructed according to our present invention. This arrangement consists of a supply reel 2| from which the steel strip I is fed to a takeup reel 23 along a preset path through one or more guide blocks 25 and past a plurality of operating stations. At the first of these stations, the strip I passes through the windings 3a and past the loop 3b of the heating coil 3 to be heated to its hardening temperature in the manner described above, it being noted that while portions of the strip I are being heated to the hardening temperature by the loop 3b, succeeding portions thereof are simultaneously heated to the Curie point by the turns 3a. Thereafter, the strip passes on through a water-cooled quench block 21 which quenches it at the second station. The strip I then advances to the third station where it is passed through a second heating coil 29 of two or three turns similar to the turns 3a and preferably operating at a lower power than the coil 3 for the purpose of heating the strip to its drawing or tempering temperature. An additional quench block 3| at a fourth station then provides final cooling. Any suitable motor (not shown) coupled to the takeup reel 23 and to a pair of drive rollers 33 may be employed for advancing the strip I continuously past the several operating stations.

Although we have shown and described but two form of heating coils constructed according to our invention and one arrangement or system in which such heating coils are utilized, it will undoubtedly be apparent to those skilled in the art that many other forms of heating coils and systems are possible. For example, instead of making the turns 3a and the loop 3b of the winding 3 all of the continuous conductor, they may be made as two separate and discrete coils each connected either to the same or to different sources of radio frequency energy. In the latter case, the two energy sources may be of the same or different frequencies, as may be found most suitable. It is also possible to provide, in place of the inductor coils herein described, a simple solenoid or winding arranged at a suitable critical angle with respect to the strip I to provide proper component fields one of which will heat by hysteresis loss and the other by eddy current loss. Other similar variations and changes will, no doubt, suggest themselves to those skilled in the art. We therefore desire that our invention shall not be limited except insofar as is made necessary by the prior art and by the spirit of the appended claims.

We claim as our invention:

1. A unitary inductor heating coil comprising a winding of at least one turn adapted to set up a magnetic field extending parallel to its axis, and means for setting up a second magnetic field which extends in a direction substantially at a right angle to that of said first named field, said means consisting of only a partial turn loop which integral with and which extends laterally from said turn in contiguous relation therewith, said loop lying in a plane substantially parallel to said axis and itself having an axis substantially normal to said first named axis.

Stllii'c'ii KUUWI 2. A unitary inductor heating coil comprising a winding of at least one turn adapted to set up a magnetic field extending parallel to its axis, and means for setting up a second magnetic field which extends in a direction substantially at a right angle to that of said first named field, said means consisting of only a partial turn loop which is integral with and which extends laterally from said turn in contiguous relation therewith, said loop lying in a plane substantially parallel to and entirely to one side of said axis and itself having an axis substantially normal 5 to said first named axis.

RUDOLPH A. BJERWIRTH. CYRIL N. HOYLER. 

